Phenolic acid and antioxidant activity evolution during kernel development of colored corn grain and relationship with mycotoxin containation

Corn (Zea mays L.) is one of the most cultivated and consumed cereal in the world. Corn red and pink ear rots are two of the major fungal diseases affecting corn production worldwide and therefore likely responsible for mycotoxin contamination. There is renewed interest in the identification of naturally occurring mechanisms which can reduce mycotoxin accumulation. Several constitutive or pathogen-induced plant endogenous compounds can inhibit mycotoxin biosynthesis. Phenylpropanoids and in particular phenolic acids, could play a role in this type of resistance mechanism as suggested by their ability to reduce in vitro fungal growth and mycotoxin accumulation. In this investigation, Total Antioxidant Activity (TAA), free and cell wall-bound phenolic acids were analyzed during kernel development of four maize open-pollinated varieties and two representative hybrids, cultivated at the same site and characterized by a wide range of colors (dark red, red, yellow and white). Maize ears were randomly handpicked from plants at four growth stages, namely: end of the silking stage (about 5 days after silking (DAS)), blister stage (about 7 DAS), dough stage (about 32 DAS) and harvest maturity (about 75 DAS). TAA and phenolic acids were determined using QUENCHER and LC-MS/MS methods, respectively. Finally, an evaluation of the protective effects of phenolic acids towards mycotoxin contamination was employed. TAA, free and cell wall-bound phenolic acids showed significant differences among corn types at different developmental stages. On average, a significant decrease in TAA, free and cell wall-bound phenolic acid content was observed from the end of the silking stage to harvest maturity. Ferulic, p-coumaric and caffeic acids were the main cell wall-bound phenolic acids during kernel development, while chlorogenic acid was the main free phenolic acid. A significant negative correlation was observed between free phenolic acids and TAA at the beginning of kernel development and deoxynivalenol contamination at harvest maturity, while no significant correlation was observed with fumonisin contamination. The findings on phenolic acids provide insight into their evolution during kernel development, evidence of their correlation with mycotoxin contamination and information about bioactive compound content of maize varieties and hybrids characterized by a wide range of color.